There are known deceleration controllers for vehicles. For example, in Japanese Kokai Patent Application No. Hei 10[1998]-278762, a safe vehicular speed for making a curve is computed based on a given turning condition of the vehicle and an allowable level of lateral acceleration preset according to a road-surface friction coefficient. The speed is automatically reduced to a safe vehicular speed, or lower, by an automatic braking system if the vehicle is about to exceed the safe vehicular speed in order to prevent spinning, drifting and overturning.